Network device interface for digitally interfacing data channels to a controller via a network

ABSTRACT

The present invention provides a network device interface and method for digitally connecting a plurality of data channels, such as sensors, actuators, and subsystems, to a controller using a network bus. The network device interface interprets commands and data received from the controller and polls the data channels in accordance with these commands. Specifically, the network device interface receives digital commands and data from the controller, and based on these commands and data, communicates with the data channels to either retrieve data in the case of a sensor or send data to activate an actuator. Data retrieved from the sensor is then converted by the network device interface into digital signals and transmitted back to the controller. In one advantageous embodiment, the network device interface uses a specialized protocol for communicating across the network bus that uses a low-level instruction set and has low overhead for data communication.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.09/735,146, filed Dec. 12, 2000 now U.S. Pat. No. 6,708,239, entitled:NETWORK DEVICE INTERFACE FOR DIGITALLY INTERFACING DATA CHANNELS TO ACONTROLLER VIA A NETWORK, which claims priority from U.S. ProvisionalPatent Application Ser. No. 60/254,136, filed on Dec. 8, 2000 having thesame title, the contents of which are incorporated herein by reference.

FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with government support under CooperativeAgreement No. NCCW-0076 awarded by NASA. The government has certainrights in this invention.

FIELD OF THE INVENTION

The present invention relates generally to network device interface and,more particularly, to an apparatus and method for digitally interfacingdata channels with a controller over a common network bus.

BACKGROUND OF THE INVENTION

In many industries today, monitoring systems are used to assess eitherpossible system failures or the affects of environment and otherexternal forces on an object of interest. For example, in the avionicsindustry, monitoring systems are employed to monitor parameters, such asstrains, acceleration, pressures, corrosion, and temperatures at variouscritical structural locations on aircraft. Similarly, such monitoringsystems could be used in the automobile industry to control and monitoreverything from on/off occupant controls to drive-train controls andmultimedia systems.

Many of these conventional monitoring systems use a plurality of remotedevices, such as sensors, actuators, and subsystems that are placedabout the object being monitored at the critical locations. Further,many of these conventional monitoring systems include either one orseveral controllers connected to each of the remote devices forreceiving data from the remote devices and sending commands to theremote devices. During operation, the controllers acquire data from thevarious sensors. The controllers also activate the actuators to performfunctions on the object.

Although these conventional monitoring systems provide a way to monitorcritical structures of an object, they do have some drawbacks. Forexample, many of the conventional monitoring systems use dedicatedwiring and signal conditioning to connect each of the remote devices tothe controller. Additionally, many of the remote devices are typicallyanalog, and data received from the remote devices is typically in analogform.

In many industries today, including the avionics and automotiveindustries, the complexity of the network may make many conventionalmonitoring systems impractical for a number of reasons. Specifically,the dedicated wiring and signal conditioning can be expensive, bulky,heavy and hard to install and maintain. This is especially critical inaircraft applications, where weight and size concerns are at theforefront. Further, in the automotive industry, the added wiring may addweight and cost to the car.

Additionally, as stated, many conventional monitoring systems transmitdata in an analog format. Typically, analog signals are susceptible tonoise introduced into the signals during data transmission. Given thatmany of the transmitted signals have a low amplitude to start with, thisnoise can corrupt the signal and decrease the signal to noise ratiolevels that cause loss of resolution in the signal. Further, as many ofthese remote devices are scattered a fair distance from the controller,the electrical lines connecting the remote devices to the controller maybe sufficiently long to cause signal degradation due to DC resistance inthe wiring.

In light of this, it would be advantageous to replace the dedicatedwiring and the analog transmission with a common bus and use digitaltransmission of data. But, many conventional digital networks sufferfrom a variety of problems themselves. For example, many existingdigital networks demand complicated protocols requiring processors and,thus, forcing unacceptably large or costly remote devices. Processorbased sensing devices may also have problems taking samples of analogdata, or causing an actuator to take an action, at exactly the righttime. Complicated protocols also introduce overhead into the messages onthe bus that are not necessary for data acquisition and control. Thisoverhead can severely limit the number of data samples that can betransmitted on the bus. These networks also have other problems. Forexample, they generally do not support both acquisition and control, andthey typically only support short network lengths. Further, theseconventional networks typically have bulky network device interfaces,slow network data rates, or a low network device count. Additionally,many computer systems that include digital networks do not operate in atime-deterministic manner. These computer systems generally lack thecapability to schedule a trigger command to the network components thatrepeats or is interpreted and executed with any precision timing.

In light of the foregoing, it would be advantageous to provide a networksystem that allows network components to digitally communicate over aninexpensive, simple and high-speed, yet robust, network line with asimple, low overhead message protocol, small component size and low wirecount. The network system would also advantageously operate without theuse of a microcontroller or processor for the network devices. Also, thenetwork system would support both acquisition and control, and becapable of acquiring or converting data simultaneously from thenetworked components. Further, the network system would allow for highcomponent counts, longer network lines and insure time determinism in aprecise manner.

SUMMARY OF THE INVENTION

A brief definition of network objects here is necessary to understandand avoid confusion in this specification. The first network object tobe defined is the bus controller. The bus controller is network devicethat sends commands on the network bus. All other devices on the networklisten to the bus controller and take actions based on the commands ofthe bus controller. A network device is any device on the network thatis not a bus controller. A network device is often referred to as aremote device throughout this disclosure. A Network Device Interface(NDI) is a component of a network device. An NDI listens to the buscontroller and any other traffic on the bus, and depending on thetraffic on the network bus, performs an action or causes the networkdevice to perform an action. Most NDIs will be connected to at least oneor more data channels. A data channel is a sensor, an actuator, a sensorand signal conditioning, an actuator and signal conditioning, or otheranalog or digital system. A data channel is a component of or isconnected to the network device.

As described in greater detail below, the present invention remediesthese and other problems by providing a network device interface (NDI)for connecting various data channels, such as sensors, actuators, andsubsystems, to a common controller for transmission of commands and datato and from the data channels and the controller. Importantly, the NDIdevice of the present invention connects various data channels to thecontroller via a common network, thereby permitting the various datachannels to share the same wiring for communicating with the controller.Further, the NDI of the present invention can interface to differenttypes of data channels, which can be analog-to-digital ordigital-to-analog or other. Sensors are connected to the NDI asanalog-to-digital data channels and actuators are connected to the NDIas digital-to-analog data channels. The NDI of the present invention iscapable of taking the digital data from an analog-to-digital channel,formatting it according to the proper protocol, and transmitting it ontothe network according to the protocol. The NDI of the present inventionis also capable of taking digital data from the network, providing it asdigital data to a Digital-to-Analog converter (D/A), and causing the D/Ato convert the data to an analog signal. It is possible for otherembodiments of the NDI to accept or produce analog signals directly toand from its data channels. By transmitting the data across the networkin a digital format, the commands and data are less susceptible to noiseand degradation.

Further, the NDI device of the present invention operates in conjunctionwith a data protocol that allows the controller to communicate witheither one or several network devices at a time across the network.Importantly, the data protocol used by the NDI device of the presentinvention has a fixed, low-level instruction set. Due to the simplicityof the protocol, the NDI device of the present invention is not requiredto be a high-level processor. Instead, in one preferred embodiment, theNDI device of the present invention is a state machine implemented as anApplication Specific Integrated Circuit (ASIC). An advantage of using astate machine to implement the NDI device instead of a micro-controlleror processor is that many processes can occur simultaneously, which aidsthe NDI device to be time deterministic and fast.

Advantageously, in one embodiment, the present invention provides anetwork device interface capable of communicating commands and databetween a controller and a data channel using either synchronous orasynchronous communication. In this embodiment, the NDI device includesa receiver for receiving messages from the controller via the commondigital bus. The NDI device of this embodiment further includes aninterface for providing commands to the associated data channel inresponse to messages received by the receiver and for receiving datafrom the associated data channel. Additionally, the NDI device includesa transmitter for transmitting messages to the controller via the commondigital bus. Importantly, the NDI device further includes a synchronousnetwork bus clock detector.

In operation, when data is received from the controller, the clockdetector of the NDI device of the present invention determines whether aclock signal accompanies the data from the controller. If a clock signalis present, then the controller is communicating in synchronous mode. Inthis instance, the NDI device uses the clock signal to provide commandsand data to and receive data from the data channel. Further, thetransmitter of the NDI device of the present invention uses the busclock signal to transmit data to the controller.

However, if the clock detector of the NDI device does not detect a clocksignal associated with the data sent from the controller, the NDI devicedetermines that the bus controller is operating in the asynchronousmode. In this instance, the NDI device provides commands and data to andreceives data from the data channel in an asynchronous mode independentof a bus clock. Further, the transmitter of the NDI device of thepresent invention transmits data to the controller asynchronouslyindependent of a bus clock in the synchronous mode.

In one embodiment, the controller provides synchronous clock signals viaa common clock bus. In this instance, the clock detector of the presentinvention receives the synchronous clock signals and analyses thesignals to determine whether it is being sent at the same rate as thedata bits. If so, the clock detector of the network device interfacedetermines that the controller is operating in the synchronous mode.

Additionally, in some embodiments, the network device interface of thepresent invention may further include a bit rate detector connected tothe common digital bus. In this embodiment, if the controller isoperating in an asynchronous mode, the controller is transmittingcommands and data at a certain bit rate. The bit rate detector of thepresent invention detects the bit rate, and the NDI device uses this bitrate to send commands and data to the data channel and receive data fromthe data channel. Further, the transmitter of the present invention usesthe detected bit rate to transmit data back to the controller.

In addition to transmitting data in an asynchronous mode at a definedbit rate, the controller may also alter the bit rate duringcommunication. In this embodiment, the controller may initially transmita first message to a data channel at a predetermined bit rate. In thisembodiment, the clock detector will not detect a synchronous clocksignal, but the bit rate detector will detect the first bit rate atwhich the message is transmitted by the controller. Based on this firstbit rate, the network device interface of the present invention usesthis bit rate to send commands and data to the data channel and receivedata from the data channel. Further, the transmitter of the presentinvention uses the detected first bit rate to transmit data back to thecontroller.

After the first or several messages are sent at the first bit rate, thecontroller may alter the bit rate and send a second message at a secondbit rate. In this embodiment, the bit rate detector of the NDI devicewill detect the second bit rate at which the message is transmitted bythe controller. Based on this second bit rate, the NDI device of thepresent invention uses this bit rate to receive commands and argumentsfrom the bus controller and send data back to the bus controller.

In one embodiment, the controller may send an example message at analtered bit rate from the bit rate previously used for sending commandsand data. In this embodiment, the bit rate detector of the NDI devicedetects the change in bit rate and the transmitter of the NDI devicetransmits data back to the controller at the new bit rate thereby,signifying that the bit rate has been altered. Further, in anotherembodiment, the controller may send a baud select command that definesthe bit rate at which messages are to be transmitted.

As mentioned, the NDI device of the present invention operates inconjunction with a protocol. In one embodiment, the protocol uses aplurality of different addresses to address either one or several datachannels at the same time. For example, in one embodiment of the presentinvention, the protocol uses a logical address to address an individualdata channel, a group address to address a number of data channels, anda global address to address all data channels at the same time. In thisembodiment, the logical and group masks are stored in a memory deviceassociated with the NDI device of the present invention. The group masksare an efficient way for the NDI device to store a list of groupaddresses for each channel. A group mask is constructed that comprises aplurality of bits for each data channel. Each bit of the mask isassociated with a respective group and has a first state indicating thatthe respective data channel is a member of the group and a second stateindicating that the respective data channel is a nonmember of the group.The mask is also stored in the memory associated with the network deviceinterface.

In this embodiment, whenever a command or data is sent it will includeeither a logical, group, or global address. For each command or datamessage that is sent, the address associated with the message isanalyzed by the NDI device. If the address is global, the NDI devicewill implement the command. Likewise, if the address is logical andcorresponds to the logical address of a data channel associated with theNDI device, the NDI device will implement the command. If the address isa group address, the NDI device of the present invention will determineif a data channel associated with NDI device is a member of the groupdefined by the group address by analyzing the mask associated with therespective data channel. The network device interface will onlyimplement the command if the data channel is a member of the grouphaving the group address.

As discussed above, the NDI device of the present invention is capableof operating in either a synchronous or asynchronous mode. Further, thecontroller is capable of providing a group address to send a command toa plurality of data channels at the same time. A problem arises,however, when the NDI devices connected to each data channel areoperating in asynchronous mode, in that it is difficult to synchronizethem such that they apply the command associated with the group addressat the same time to the respective data channels connected to them. Inlight of this, in one embodiment, the NDI devices can be synchronized,even though they are operating in asynchronous mode.

Specifically, in one embodiment of the present invention, the controllertransmits a command to a plurality of data channels, wherein the commandcomprises a plurality of bits having a value defined by a transitionbetween first and second states. In this embodiment, each of the NDIdevices of the present invention commences implementation of the commandat the same predetermined time relative to the transition that definesthe value of a respective bit of the command such that the plurality ofnetwork device interfaces perform the command simultaneously in atime-deterministic manner. In one further embodiment, the controllertransmits a command comprising a sync portion, a message body and aparity bit. In this embodiment, the NDI devices of the present inventioncommence performance of the command coincident with the transition thatdefines the value of the parity bit. Further, in another embodiment, thecontroller transmits a command comprising a start bit, a command field,an address filed having an unused last bit set to 0, and a stop bitset 1. In this embodiment, the NDI devices of the present inventioncommence performance of the function at each data channel coincidentwith the transition from the unused bit of the address field to the stopbit.

In addition, as described above, in the synchronous mode, the controllertransmits a synchronous clock signal on the common digital bus. In thisembodiment, the NDI device of the present invention may also provide forsynchronous implementation of commands between several network deviceinterfaces by using the synchronous clock signal. Specifically, in thisembodiment, the controller transmits a command to a plurality of datachannels, where the message comprises a plurality of bits having a valuedefined by a transition between first and second states. Further, thecontroller transmits a synchronous clock signal comprised of a pluralityof clock pulses from the controller to the plurality of data channelssimultaneous with the message. In this embodiment, the plurality of thenetwork device interfaces will commence performance of the command atthe same predetermined time as defined by a respective clock pulsewhich, in turn, is defined based upon a predetermined relationship to arespective bit of the message.

For example, in one embodiment, the network device interfaces commenceperformance in synchronization with the first clock pulse following therespective bit of the message. Specifically, in one embodiment, themessage transmitted has a plurality of bits having a value defined by atransition between a first state and a second state and the messagedefines a sync portion, a message body and a parity bit. In thisembodiment, the network device interfaces commence performance of thecommand at the same predetermined time as defined by a respective clockpulse which is, in turn, defined based upon a predetermined relationshipto the transition that defines the value of the parity bit of themessage.

As discussed, the NDI device of the present invention operates inconjunction with a protocol that has a fixed, low-level instruction setthat, in turn, allows in some case for use of simplified controllers andnetwork device interfaces on network devices. Specifically, in oneembodiment, the present invention provides a protocol stored on acomputer-readable medium. The protocol is used for transmitting commandsand data between a controller and a network device interface across acommon digital network. Importantly, the protocol includes at least oneof a command and a data structure for sending respective commands andarguments to data channels. The data structure is also used to send datafrom data channels to the bus controller.

In light of this, the present invention also provides a serial,multiplexed communication system that uses state machines. Specifically,the communication system of the present invention includes a controllerfor issuing a plurality of commands and a plurality of data channels forperforming predefined functions in response to the commands. Connectingthe controller and network device interface is a common digital bus forsupporting communication therebetween. Further, the communication systemincludes a plurality of network device interfaces, one of which isassociated with each data channel for interconnecting the respectivedata channels with the common digital bus. In this embodiment, eachnetwork device interface comprises a state machine and is independent ofa processor.

As mentioned previously, in the synchronous mode, the controllerprovides a synchronous clock signal across the network bus to thenetwork device interfaces. In the synchronous mode, the synchronousclock is used as the clock signal for transmitting data. However, someA/D and D/A converters, as well as some signal conditioning devices,cannot operate at the clock speed set by the synchronous clock. In lightof this, in one embodiment of the present invention, the network deviceinterface of the present invention may include a clock divider. Theclock divider may either be connected to the synchronous clock signaloutput by the controller or it may be connected to a local oscillator.

Specifically, in this embodiment, there is a bus controller, sending asynchronous clock signal and commands to the network devices at onefrequency, and NDI devices listening to the synchronous clock and datafrom the bus controller. The NDI devices are converting the data andcommands from the bus controller into the proper format expected by thedata channels connected to the NDI devices, and the NDI devices aresimultaneously providing the divided second clock signal to datachannels, such that the data channels operate in accordance with thesecond clock signal frequency to convert data while the controller andNDI devices operates in accordance with a first clock frequency to sendcommands and data over the network bus.

In one further embodiment, the NDI device of the present inventionfurther includes a method for synchronizing the dividers associated witheach NDI device with those of all other NDI devices connected to thecommon digital bus. Specifically, as stated previously, in someembodiments, the controller will send a group address so that a commandis performed on a plurality of data channels at the same time. In orderfor this to occur, however, all of the clock dividers provided to datachannels that use the divided clock located at each NDI device must besynchronized. In light of this, in one embodiment, the controller sendsa first clock signal across the common digital bus. Further, thecontroller commands each of the dividers to synchronize the transmissionof their respective second clock signals with an edge of the first clocksignal such that individual second clock signals provided by each of thedividers is synchronized with respect to the first clock signal tothereby synchronize each of the converters.

In addition to operating in accordance with different clock signals,some A/D and D/A converters also operate in accordance with specializedcommands that are different from the commands used by the controller. Inlight of this, the network device interface of the present invention mayinclude a special feature used to provide the specialized commands forthe converter. This feature is called command translation. As such,during operation, the NDI device of the present invention receivescommands and data from the controller in accordance with a first set ofcommands and converts the command in accordance with a second set ofcommands for application to the converter. Further, the NDI device ofthe present invention may send data received from the converter acrossthe common digital bus in accordance with the first set of commands.

The preferred protocol for the NDI devices uses Manchester encoding ofnetwork data bits to help allow miniaturization of the NDI devices. Itmust be understood that for any device to receive asynchronous serialdata, it must be able to acquire the timing of the data sequence fromthe serial data stream. Normally, the receiver of the serialasynchronous data must have a local oscillator to cause its receiver tooperate, and recover the timing information from the serial data. Oncethe timing information has been extracted, the asynchronous receiver isable to receive serial data at certain rates, plus or minus a certaindeviation from these rates, given this local oscillator frequency.Manchester encoding of serial data causes a transition from high to lowor low to high in the center of every bit. This makes it easy to extractthe necessary timing information from the serial data stream. Because itis so easy to extract the timing information from the Manchester encodedserial data stream, a relatively large deviation from the expected datarate, based on the local oscillator can be tolerated. This tolerance torelatively large deviations from the expected data rates allows each NDIreceiver to use a low accuracy local oscillator to receive theManchester encoded data. Low accuracy local oscillators can be madeextremely small. Current embodiments of adequate local oscillators areonly about 1×1.5 millimeters. This aids in making miniature NDI devises.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a networked system for transmittingcommands and data digitally between a controller and a plurality of datachannels via a network bus according to one embodiment of the presentinvention.

FIG. 2 is a block diagram of the operations preformed to transmitcommands and data digitally between a controller and a plurality of datachannels via a network bus according to one embodiment of the presentinvention.

FIGS. 3A and 3B are generalized block diagrams of a NDI device fordigitally communicating commands and data between data channels and acontroller across a network bus according to one embodiment of thepresent invention.

FIG. 4 is a block diagram of the operations performed by the NDI toretrieve data from a remote devices and illustrates the ability of theNDI device to perform multiple tasks at the same time whilesimultaneously communicating with the bus controller according to oneembodiment of the present invention.

FIG. 5 is a block diagram of the operations performed to translatecommands sent by a controller to a remote device into specializedcommands used by a converter connected to the NDI, such that thecontroller may communicate with the remote device according to oneembodiment of the present invention.

FIG. 6 is a block diagram of the operations performed to determinewhether a controller is operating in either a synchronous orasynchronous mode according to one embodiment of the present invention.

FIG. 7 is a block diagram of the operations performed to determine thebit rate at which a controller is transmitting commands and dataaccording to one embodiment of the present invention.

FIG. 8 is a block diagram of the operations performed by an NDI whilethe bus controller is assigning logical addresses and group addresses tothe network device according to one embodiment of the present invention.

FIG. 9 is graphic diagram illustrating the synchronization of aninternal free running clock provided by the NDI device to a data channelin order to synchronize the free running clocks of multiple datachannels attached to the network through multiple NDI devices accordingto one embodiment of the present invention.

FIG. 10 is a schematic diagram of an electrical network system accordingto one embodiment of the present invention implemented in an aircraft.

FIG. 11A is a block diagram of the connection of the NDI device of thepresent invention to a successive approximation A/D that uses a convertsignal from the NDI device to acquire data with precise timing,according to one embodiment of the present invention.

FIG. 11B is a block diagram of the connection of the NDI device of thepresent invention to a digital filter and decimator and a sigma/deltaA/D that uses the synchronized divided clock and possibly thesynchronize signal to acquire data with precise timing, according to oneembodiment of the present invention.

FIG. 11C is a block diagram of the connection of the NDI device of thepresent invention to a successive approximation A/D and signalconditioning with switched capacitor filters, where the switchedcapacitor filters require both the convert and divided clock signals toacquire data with precise timing, according to one embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention now will be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown. This invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein; rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art. Likenumbers refer to like elements throughout.

As described above, many conventional data acquisition and controlsystems use individual wiring to connect remote devices, such assensors, actuators, and subsystems, to a central controller for dataacquisition and control. Due to the large number of remote devices, thetotal of the individual wiring for each of these devices can beexpensive, bulky, heavy, and difficult to install and maintain. Further,since many of these remote devices are analog, signals to and from theremote devices are susceptible to noise and signal degradation.

As described in greater detail below, the present invention remediesthese and other problems by providing a network device interface (NDI)for connecting various data channels, that can be sensors, actuators,and subsystems, to a common controller for transmission of commands anddata to and from the data channels and the controller. Importantly, theNDI device of the present invention connects various remote devices tothe controller via a common network, thereby permitting the variousremote devices to share the same wiring for communicating with thecontroller. Further, the NDI of the present invention can interface todifferent types of data channels, which can be analog-to-digital ordigital-to-analog or other. Sensors are connected to the NDI asanalog-to-digital data channels and actuators are connected to the NDIas digital-to-analog data channels. The NDI of the present invention iscapable of taking the digital data from an analog-to-digital channel,formatting it according to the proper protocol, and transmitting it ontothe network according to the protocol. The NDI of the present inventionis also capable of taking digital data from the network, providing it asdigital data to a Digital-to-Analog converter (D/A), and causing the D/Ato convert the data to an analog signal. It is possible for otherembodiments of the NDI to accept or produce analog signals directly toand from its data channels. By transmitting the data across the networkin a digital format, the commands and data are less susceptible to noiseand degradation.

Further, the NDI of the present invention operates in conjunction with adata protocol that allows the controller to communicate with either oneor several network devices at a time across the network. Importantly,the data protocol used by the NDI device of the present invention has afixed, low-level instruction set. Due to the simplicity of the protocol,the NDI device of the present invention is not required to be ahigh-level processor. Instead, in one preferred embodiment, the NDIdevice of the present invention is a state machine implemented as anApplication Specific Integrated Circuit (ASIC). An advantage of using astate machine to implement the NDI instead of a micro-controller orprocessor is that many processes can occur simultaneously, which aidsthe NDI to be time deterministic and fast.

As mentioned above, the NDI of the present invention is used as aninterface between a common controller and various network devices thatare connected to the controller by a common network. FIG. 1 is anillustration of one embodiment of the implementation of the interface ofthe present invention. This illustration is provided so that a morecomplete understanding of the present invention may be appreciated. Itmust be understood that the present invention is not limited to thisconfiguration and may be embodied in many different network systems. Thecurrent embodiment of the NDI uses the RHAMIS-HS protocol, however,other embodiments contemplated by this disclosure may use otherprotocols.

With regard to FIG. 1, a general embodiment of a networked system 30 inwhich the present invention is used is shown. Specifically, thenetworked system includes a master controller 32 such as high-levelprocessor or personal computer that processes data from and sendscommands and data to data channels 34, such as sensors, actuators, andsubsystems, located at desired points in the network. Importantly, thenetworked system further includes a network controller 36 connectedbetween the master controller 32 and a network bus 38, and either one orseveral NDI devices 40 connected between the network bus and the datachannels. Connecting the network controller and NDI devices to thenetwork bus are respective transmitters, 42-46, and receivers 48-52. Afirst transmitter 42 connected between the network controller and thenetwork bus transmits commands and data on the network, while a secondtransmitter 44 also connected between the network controller and networkbus may be used in some embodiments to transmit a synchronous clocksignal.

In normal operation, the remote devices that are sensors are connectedto a specific object under study and sense characteristics of the objectsuch as temperature, strain, flex, speed, air flow, etc. Further, theremote devices that are actuators are connected to mechanical membersand other structures to operate on the object under test. One or severalof the remote devices are connected to a single NDI device of thepresent invention via individual data channels containing converters andsignal conditioning devices. Further, either the master controller orthe network controller may be configured to send data and commandsacross the network to the various network devices. Given that both ofthese controllers are capable of such action, the generic term buscontroller is used in the discussion below to describe operations thatmay be performed by either the master or network controller.

With reference to FIG. 2, to acquire data from a sensor or activate andactuator, the controller sends commands and data digitally across thenetwork to the remote devices, where the command and data is designatedfor either one or a group of the data channels on the remote devices.(See step 200). The commands and data are transmitted across the networkusing a data protocol. The NDI devices of the present invention receiveand interpret the data and commands using the structure of the dataprotocol. (See step 210). Further, the NDI devices of the presentinvention determine whether the commands and data are designated for thedata channels connected thereto. (See step 220). If so, the NDI eitheracquires data from the designated data channel if it is a sensor orcommands the data channel to perform a conversion if it is an actuator.(See step 230). Analog data retrieved from the sensor channels is firstconverted into digital data, (see step 240), and then converted into theproper format according to the data protocol. Further, the digital datais transmitted to the controller. (See step 250).

As illustrated in FIGS. 1 and 2, the NDI device of the present inventionoperates as an interface between the bus controller and the datachannels. Importantly, the NDI device of the present invention iscapable of accepting digitized, analog data signals from data channelsfor transmission across the network bus. The NDI can also accept digitaldata from the bus controller and present it to a data channel. Then aD/A converter can change the data to an analog signal. It is possiblethat some data channels would accept and use the digital data directlywithout converting it to analog. Some embodiments of an NDI may have ananalog-to-digital (A/D) converter and a D/A converter integrated intothe NDI, thereby being configured to accept or present analog signalsfrom or to data channels. The NDI device of the present invention alsooperates in conjunction with a selected data protocol to properlyreceive and decode or format and send data efficiently via a networkbus.

Further, the NDI device of the present invention provides additionaloperations and features, such as programmable trigger commandconversion, and clock signals, that allow the controller to communicatewith different types of devices that compose data channels.Additionally, the NDI device of the present invention includes storedinformation and procedures for configuring the data channels connectedthereto. A/D and D/A converters are examples of components of datachannels that may need to be programmed or configured. The NDI device ofthe present invention may also provide a local clock signal to datachannels that is some fraction or multiple of the local oscillator orsynchronous bus clock. The local clock signals of many or all NDIdevices on a network can be synchronized by the bus controller. Further,the NDI device of the present invention operates in conjunction with thedata protocol to provide a unique logical address and group addressesfor each of the data channels, such that the data channels may be eitheraddressed individually, in a synchronized group, or all together.

In addition to allowing for data communication between the controllerand remote devices and data channels having different configurations,the NDI device of the present invention also allows for datacommunication across the bus network using different data transmissionmodes. Specifically, in one mode of the present invention, the NDIdevice of the present invention operates in conjunction with thecontroller in a synchronous mode, in which a synchronous clock signalprovided by the controller is used by the NDI device to receive commandsand data from the bus controller. This same synchronous clock signal isused by the NDI to send data to the bus controller or other networkdevices.

As a note, the NDI devices typically do not transmit the synchronous busclock signal back to the bus controller. Instead, the NDI devicestypically only clock data out on received edges of the synchronous busclock signal in the synchronous mode. Generally, only the bus controllertransmits the synchronous bus clock signal. Further, the bus controllerwill typically include an asynchronous receiver for receiving data fromthe NDI devices.

In another mode, which can be the same or different embodiment, the NDIdevice operates in conjunction with the controller in an asynchronousmode. In this embodiment, the NDI device of the present inventionanalyzes and determines the bit rate at which the controller istransmitting data on the network bus and then uses this bit rate toretrieve commands and data from the bus controller and send data to thebus controller or other network devices. Also in the asynchronous mode,the NDI device may still synchronize data conversion on data channelslocated on different NDI devices. Data conversion is synchronized on theseparate data channels by having it occur on or very shortly after thechanging edge of a special bit in a command from the bus controller.

These and other advantages are realized by the NDI device of the presentinvention; one embodiment of which is illustrated in FIGS. 3A and 3B.Specifically, FIG. 3A illustrates a generalized block diagram of a NDIdevice 40 according to one embodiment of the present invention. Asillustrated, the NDI device of the present invention is connectedbetween the network bus 38 and remote devices 34 and 36, such asillustrated previously in FIG. 1. In this embodiment, one of the remotedevices 34 is a sensor and the other remote device 36 is an actuator orsimilar device. Both remote devices contain signal conditioning devices,58 and 60, for conditioning analog signals. With regard to remote device34 the signal conditioning 58 is for a sensor signal. The signalconditioning for an actuator is shown in 60. Signal conditioning caninclude but is not limited to amplifiers, filters, attenuators, etc.

Importantly, connected between the remote devices and the NDI device ofthe present invention are A/D and D/A converters, 62 and 64,respectively. The A/D converter 62 is connected between the NDI deviceand the sensor 34. The A/D converter converts analog signals from thesensor channel into digital data for input into the NDI device.Similarly, the D/A converter 64 is connected between the NDI device andthe actuator device 36 and converts digital signals from the NDI deviceinto analog signals for input into the actuator channel. It is possiblethat some sensors and some actuators could produce or accept digitalsignals directly so that the A/D 62 or D/A 64 is not necessary.

As illustrated previously in FIG. 1, the NDI device of the presentinvention is connected to the network bus via a first receiver 50 thatreceives commands and data from the controller. A second receiver 52 isalso provided for receiving the optional synchronous clock signal fromthe controller if the network is operated in synchronous mode. Atransmitter 46 is also connected between the NDI device of the presentinvention and the network bus for transmitting data to the controller.Further, a memory device 66 and a local oscillator 68 are connected tothe NDI device of the present invention. Different embodiments of theNDI device could integrate some or all of the following: the receivers,transmitters, local oscillator, and memory.

FIG. 3B provides an illustration of the various control logic componentsof the NDI device 40 according to one embodiment of the presentinvention. Specifically, the NDI device of this embodiment of thepresent invention includes ports, 70 and 72, for connecting to the datachannels, 34 and 36. These ports are typically serial ports, but may beparallel ports in some embodiments. The ports of the NDI device arecontrolled by individual port controllers, 74 and 76. Data linesincorporated in each port include a data output line 78 referred to asSerial MOSI (master out slave in), a chip enable or chip select line 80referred to as CE, a clock signal line 82 referred to as Serial CLK, anda trigger 84. As illustrated, the data output line 78 consists of aconfiguration data output line 78 a and a data out/special command outline 78 b. The configuration data output line 78 a is used as describedlater for configuring the data channel at power up. Further, the dataout/special command out line supplies data from the bus controller tothe data channel. The output select line 79 toggles a select switch 86between the configuration data output line and Serial out data linedepending on whether the NDI device is in power up mode or in normaloperation.

As mentioned, the NDI device of the present invention further includes adata stack 88 defined as a plurality of data registers creating amemory. The data stack is used for storing digital data acquired from adata channel. A data stack can also be used for storing data from thebus controller to send to a data channel. The data stack is typicallyoperated as a last-in-first-out (LIFO) device, where the last valueplaced in the data stack is the first value retrieved from the stack.This way, no matter what the stack size, data will be returned to thebus controller by different NDI devices in the same order. There isminimum delay between putting a new data value on the top of the stackto when the bus controller can read it. However, there would be a largedelay if the bus controller had to read data from the bottom of a stack.

As illustrated, associated with the data stack is a stack depth register90. The stack depth register indicates the number of valid data words inthe stack at that time.

Further, internal to the current embodiment of the NDI device of thepresent invention are a status register 92 and a data select multiplexer94 for each data channel. Importantly, the status register includesinformation relating to the status of the data channel, such as whetherthe data channel is in a ready mode, whether the data channel supports acommand, or whether there is a message transmission error, etc. The dataselect multiplexer, depending on the data requested, connects either thestatus register, data stack, or stack depth register, to an output datamultiplexer 96. The data select multiplexer 94 for each channel iscontrolled by the respective port controller, 74 and 76. The output datamultiplexer 96, in turn, selects between the output of the two remotedevices or a device inventory register 98. Different embodiments of theNDI device may have different multiplexer arrangements in the NDIdevice, but the effect will always be to allow the bus controller toaccess any register for any data channel in an NDI device that it needs.

The Device Inventory block 98 is used by the NDI device to execute theDevice Inventory operations that are shown in the flow chart in FIG. 8.

Further, the NDI device of the present invention also includes anaddress decoder 100 and a command decoder 102. As described later below,these decoders receive the command and data transmitted by thecontroller, decode the commands and data, and determine whether thecommands and data are addressed to one or more of the data channelsconnected to the NDI device. If the commands and data are addressed forone of the data channels, the NDI device of the present invention willoperate on the data channel in accordance with the command. The abovecomponents are sometimes referred to herein as a device interface.

An NDI device will include a non-volatile memory indicated in FIG. 3A asmemory device 66 that will be used by the NDI to store the UUID,protocol version, number of data channels, logical addresses, groupmasks, configuration data, and other data that the manufacturer or usermay define. The communication with this memory device is illustrated inFIG. 3B by the input and output lines from the configuration register104 to the memory device. The bus controller will be able to read thememory and write to various memory locations according to the protocol.The logical address and group mask fields in memory are special. Theycan only be written to by the bus controller immediately after the NDIdevice has won a Device Inventory Competition according to the flowdiagram in FIG. 8. This allows every NDI device to be uniquelyidentified by the bus controller and then the logical addresses andgroup masks to be assigned. By mandating that a Device InventoryCompetition must be won prior to writing to these fields, it becomesvirtually impossible to accidentally change these values. This same sortof memory protection can be applied by the NDI device manufacturer toother memory fields.

At power up some of the contents of the non-volatile memory 66 areloaded into the logical and group address decoder registers 100,configuration registers 104 for the Serial ports, 70 and 72, commandtranslation registers in port controllers, 74 and 76, and some contentsare sent out the Serial ports or other parallel ports for configuringdata channels. There may be other uses for this memory data at power up.This memory can also be used by the bus controller to store user-definedinformation such as network device installation location, calibrationdata, etc. The contents of this memory are commonly called TEDs whichstands for Transducer Electronic Data Sheet.

Further, the NDI device of the present invention may include controllogic 106 for receiving commands and performing built in testing,calibration, and transitioning the NDI device between a sleep and wakemode.

As illustrated in FIG. 1, the NDI device of the present inventioncommunicates with a controller across a network bus. The discussion ofthe various operations of the present invention described below are withregard to the NDI device. Detailed operation of the master and networkcontrollers is not described herein. However, a complete detaileddisclosure of the operation of the master controller and networkcontroller is provided in U.S. Provisional Patent Application No.60/254,137 entitled: NETWORK CONTROLLER FOR DIGITALLY CONTROLLING REMOTEDEVICES VIA A COMMON BUS and filed on Dec. 8, 2000. The contents of thispatent application are incorporated in its entirety herein by reference.

As mentioned, the NDI device of the present invention provides severaladvantages. One important aspect of the NDI device of the presentinvention is self-configuration at power up of the A/D and D/Aconverters and the remote devices connected to the NDI device. Asillustrated in FIG. 1, the remote devices connected to the network busmay be numerous and spread far apart making it difficult to configurethe devices from a central location. In light of this, in one embodimentof the present invention, the NDI device includes data related to thegain, offset, filters, etc. of the signal conditioning devices, 58 and60, and data related to the A/D and D/A converters stored in the memorydevice 66, (illustrated in FIG. 3A). Specifically, in one embodiment,the NDI device of the present invention allows 16,16-bit digital wordsfrom the memory device to be output each of the ports, 70 and 72, atpower up. This aspect of the NDI device of the present invention allowsfor automatic configuration of off-the-shelf A/D and D/A converters.

The configuration data stored in the memory device is programmable bythe controller. The 16, 16-bit words can be programmed to be split into32, 8-bit bytes for output by the ports to the A/D and D/A convertersand signal conditioning. Further, the NDI device of the presentinvention can be programmed by the controller to change the Serial clock82 phase and Serial clock 82 polarity at which the configuration data isoutput at the ports, 70 and 72.

In addition to configuring the A/D and D/A converters and signalconditioning devices at power up, the NDI device of the presentinvention is also configurable to operate with different types of A/Dand D/A converters and signal conditioning devices. Specifically, thereare many types of converters, such as successive approximation A/Dconverters and sigma/delta oversampling converters. These converters mayoperate differently in terms of clocking and operational delay. Further,some signal conditioning devices, such as switched capacitor filters anddigital anti-alias filters operate differently in terms of clocking.

For example, as illustrated in FIG. 1, in the synchronous mode, thecontroller provides a synchronous clock signal across the network bus tothe network devices. In the synchronous mode, the synchronous clocksignal is used as the clock signal for transmitting network data. SomeA/D converters, such as Analog Devices' AD7714 converter need acontinuous clock signal to operate correctly. This clock is usuallylower frequency than the synchronous clock signal provided by thecontroller. In light of this, in one embodiment of the presentinvention, the NDI device of the present invention may include a clockdivider 108. The clock divider may either be connected to thesynchronous clock signal output by the controller as shown in FIG. 3B orit may be connected to a local oscillator 68, as illustrated in FIG. 3A.

This clock signal provided by the NDI device can be synchronized by thebus controller as shown in FIG. 9. The clock signal can simultaneouslybe synchronized in one, several, or all NDI devices on the bus. In theexample in FIG. 9 the internal clock frequency is shown as ¼ thesynchronous bus clock frequency. It could actually be any other fractionof the synchronous bus clock frequency.

FIG. 4 is a block diagram of the operations performed by the NDI inresponse to one particular command from the bus controller. This diagramillustrates that the NDI device is capable of doing more than one taskat a time. The ability of the NDI device to do multiple tasks at thesame time allows the NDI device of the present invention to acquire orcontrol 1 or more data channels at the same time while simultaneouslycommunicating with the bus controller.

With reference to FIG. 4, in operation, the NDI device of the presentinvention initially receives a command, (see step 310), such as Triggerand Read command, from the controller and interprets the command. If thecommand and address are intended for a data channel on the NDI devicethe NDI device begins the operations shown in steps 330 and 360 inparallel. Specifically, the NDI device sends a convert signal to thedata channel attached to the NDI. (See step 330). The rising edge ofthis data pulse occurs at the center edge of the parity bit at the endof the Trigger and Read command. The convert signal is provided to latchanalog data into the sample and hold circuitry of an A/D converter, orcan be used to cause a D/A to start a conversion process. The precisetiming of the rising edge of this signal allows many data channels toknow when to sample or convert analog data, even if the network devicesare not operating in synchronous mode.

After the convert signal is created, a short pause occurs. (See step340). This pause allows the data channel to have time to convert theanalog signal latched in its sample and hold to be converted into adigital value. In the present embodiment of the NDI device, this pauseis programmable. There are two choices. It can be only a few hundrednanoseconds long, or it can be programmed to be 6 microseconds long.

After the pause, a serial transfer occurs. (See step 350). During thisSerial transfer a programmable word is clocked out on the MOSI line.This programmable word is used to cause special A/D converters to outputdata. An example is an AD7714. As this serial transfer continues, datais returned from the data channel to the NDI device. The digital datareturned to the NDI device on the MISO line is stored in the in dataregister 89.

At the same time operational steps 330, 340, and 350 are occurring,operational steps 360, 370, and 380 are also occurring. In operationstep 360, the contents of the in data register 89 are shifted into thetop of the data stack. Next, the contents in the top of the data stackare loaded into the transmitter register. (See step 370). The lastoperation is for the contents of the transmitter register aretransmitted back to the bus controller by the NDI device's transmitter46. (See step 380).

During all of these operations, the NDI interface is providing acontinuous clock signal to the data channel. Not all data channels willuse this clock but it is available. The frequency of this clock isprogrammable. This clock signal is useful for running devices such asswitched capacitor filters, digital filters, or sigma/delta converters,etc. This clock signal continues running even when operational steps300-380 are not taking place.

In instances where the Universal Asynchronous Receiver Transmitter(UART) protocol is used, the controller transmits a command comprising astart bit, a command field, an address filed having an unused last bitset to 0, and a stop bit set 1. In this embodiment, the NDI device ofthe present invention commences performance of the function at each datachannel coincident with the transition from the unused bit of theaddress field to the stop bit.

In addition to clock and delay issues, some A/D and D/A converters alsorequire special commands. For example, some A/D and D/A converters areprogrammable to take different readings from a sensor. For instance, inone application, an A/D converter is connected to a strain gauge thatsenses strain in three dimensions. Each readable dimension isaddressable with a separate 16-bit address. Either one or all of themeasurements for each dimension may be accessed by applying theassociated 16-bit command to the converter. It may become burdensome tostore all of the bit commands in the controller and transmit them acrossthe network bus. To simplify operation of the protocol, (as discussedbelow), the NDI of the present invention maintains these specialcommands so that they do not have to be kept up with by the controlleror sent across the network. In light of this, in one embodiment, the NDIof the present invention includes the specialized bit commandsassociated with the A/D or D/A converters connected to the NDI. Withreference to FIGS. 3A and 3B, these commands are originally stored inthe memory device 66, where they are programmable. During power up,these specialized bit commands may be stored in the command decoder 102.

With reference to FIG. 5, in operation, when a remote device having aconverter with specialized commands is to be addressed, (to eitherobtain data from a sensor or in the case of an actuator, activate theremote device), the controller will send a properly formatted triggercommand along with the address of the data channel with the converter.(See step 400). (The format of commands is discussed below). When theNDI associated with the data channel receives the command and address,(see step 410) the NDI initially determines whether the remote deviceaddressed needs specialized commands. This is done by comparing theaddress received to the address associated with the data stored in thecommand decoder. (See step 420). Based on the address, the NDI of thepresent invention retrieves the proper specialized command from thecommand translation register. (See step 430). The specialized command isthen applied to the converter to either receive information, in the caseof a sensor, or activate an actuator corresponding to the command. (Seestep 440).

As briefly discussed, the controller and the NDI device of the presentinvention are capable of operating in either a synchronous orasynchronous mode. In the synchronous mode, the controller provides acontinuous synchronous clock signal. The synchronous clock signal isused by the NDI device of the present invention to clock in data fromthe bus controller and to clock data out to the controller. This allowsthe bus controller to pick any data rate between 0 bits/sec up to somemaximum bit rate.

The NDI device of the present invention can automatically detect whetherthe controller is operating in the synchronous or asynchronous mode.Specifically, with reference to FIGS. 3A, 3B, and 6, the NDI device ofthe present invention continuously checks the signal received on thesecond receiver 52 using a clock detector. (See step 500). If asynchronous clock signal is present, (see step 510), the NDI device ofthe present invention operates in the synchronous mode, (see step 520),and uses the synchronous clock signal from the controller to clock datain and clock data out. However, if the NDI device of the presentinvention does not detect a synchronous clock signal from the secondreceiver 52, (see step 510), the NDI device of the present inventionoperates in asynchronous mode. (See step 530).

As mentioned above, in asynchronous mode, the controller may operate atvarious bit rates. In light of this, in one embodiment, the NDI deviceof the present invention detects the bit rate at which the controller isoperating. Specifically, with reference to FIG. 7, in this embodiment,after the NDI device of the present invention determines that thecontroller is operating in asynchronous mode, the NDI device of thepresent invention monitors the bits of the command and data transmittedby the controller. (See step 600). The NDI device determines the timebetween receipt of each bit using a bit rate detector. After apredetermined number of bits have been received having substantially thesame time between transmissions, (see step 610), the NDI device of thepresent invention chooses and operates at the bit rate of the data beingsent to the NDI device. (See step 620). Importantly, the ability of theNDI device to detect bit rate is advantageous for fast recovery whenthere are power glitches in the networked system, or where thecontroller has transitioned from synchronous to asynchronous mode. Asecond important advantage of the automatic synchronous clock detect andautomatic bit rate detect features is that it allows a single type ofNDI device to communicate on the network using different modes ofnetwork communication. Designer of the network system can choose themode of network communication that is optimized for the particularapplication of the network system.

In one further embodiment, the bus controller can command the NDI deviceto receive and transmit data at a specific bit rate. The bus controllersends a change bit rate command followed by the bit rate the NDI devicesis to change to. After that the NDI device will receive data from andtransmit data to the bus controller at the bit rate instructed by thebus controller. Further, the controller may send an example message atthe new bit rate, and the NDI of the present invention will change tothe new bit rate before real commands and data are sent.

Another advantage of the NDI device of the present is the ability ofmany data channels on many different NDI devices on a network bus tosample or convert analog data at substantially the same time whencommunicating to the bus controller in the synchronous or asynchronousmodes. One method of synchronization of data sampling or conversion inthe asynchronous mode is accomplished by having the rising edge ofconvert signal 84, (see FIG. 3B), go high at or very shortly after thechanging center edge of the convert command from the bus controller.Some protocols call a convert command a trigger command. The ability ofthe protocol and NDI devices to take data or convert data simultaneouslyeven in the asynchronous communication mode is called isochronous.

The second method of synchronization data sampling is by providingsynchronized clock signals from each NDI device to each data channelassociated with each NDI device. The clock signals are synchronized bythe bus controller using the synchronize command, and the NDI devicessynchronize in response to the command according to the timing in FIG.9. That way all data channels using a clock signal that has a frequencythat is a divided fraction of the synchronous bus clock will all berunning nearly perfectly synchronously.

In addition to providing an interface with different types of A/D andD/A converters and different signal conditioning systems and operatingin both synchronous and asynchronous mode, the NDI device of the presentinvention can also save overhead in the transmission of data across thenetwork. Specifically, as illustrated in FIG. 3B, the NDI device of thepresent invention includes a data stack 88. In the case where the NDIdevice is connected to a sensor remote device, the data stack is an InData Stack. The In Data Stack contains data received from the datachannel. In this instance, the data stored in the In Data Stack can beread out by the controller either one word at a time, (i.e., oneregister at a time), or as a block of data, (i.e., multiple registers ata time). Reading a block of data from the data stack at a time savesnetwork overhead.

Further, in instances in which the NDI device of the present inventionis connected to an actuator remote device, the data stack is an Out DataStack. In this case, the Out Data Stack contains data transmitted by thecontroller to be output to the actuator data channel. When a triggercommand is sent to the actuator, the actuator performs a digital toanalog conversion of the word at the top of the data stack, then NDIdevice will pop the stack, and transmit the new word at the top of thestack to the D/A. Data words can be written to the Out Data Stackindividually by the controller or as a block of words. Writing a blockof data to the Out Data Stack instead of one a time saves networkoverhead.

In addition to the advantages described above, the NDI device of thepresent invention also provides additional advantages. Specifically, inone embodiment, the NDI device of the present invention operates inconjunction with a protocol that allows data channels to communicateover a simple and high-speed, yet robust, digital multi-drop network. Itmust be understood that any applicable protocol could be used inconjunction with the NDI device of the present invention. However,described below is a particular protocol that provides severaladvantages when used in the networked system 30 illustrated in FIG. 1.One important advantage being that the simplicity of the protocol allowsthe NDI device to be implemented as a state machine, as opposed to ahigh-level processor.

Specifically, the protocol is designed to insure low-level communicationcontrol interface, (i.e., network controllers and NDI devices). Theprotocol makes possible the development of controller and network deviceinterfaces that are highly miniaturized within the network. If thenetwork controller and NDI devices are implemented in an ApplicationSpecific Integrated Circuit (ASIC) or FPGA working in conjunction withthe protocol, the network controller and NDI device can respond quicklyand efficiently allowing for maximized bus efficiency. If the buscontroller or NDI device is implemented as an ASIC, the bus controllerand NDI devices can be made very small.

The protocol of the present invention also has a low-overhead commandstructure. The protocol of the present invention does not use afixed-length message. The length of the message varies depending on thecommand. This, in turn, permits the elimination of unnecessary databeing transmitted if it is not needed to execute a command. In addition,the command set is minimal and straightforward thus allowing the user toeasily pass data through the network bus with minimal manipulation.

As discussed, the NDI device of the present invention operates inconjunction with a protocol that has a fixed, low-level instruction setthat, in turn, allows in some case for use of simplified controllers andnetwork device interfaces on network devices. Specifically, the lowlevel command set allows the NDI devices to be implemented as statemachines instead of processors or micro-controllers. An example of howthe low level command set works is given here. If the bus controllerwants to read a data word from the memory of an NDI device it sends acommand to the NDI called set pointer, then follows the command with thepointer value. The NDI decodes the command and sets its memory addresspointer to be the value sent by the bus controller. The memory addresspointer only needs to be a register that latches the value sent by thebus controller. Next, the bus controller will issue the read memory wordcommand to the NDI device. The NDI device responds by accessing thememory word pointed to by its memory address pointer, and transmittingit to the bus controller. If the bus controller wants to read a block ofdata from the memory of the NDI it repeats the process multiple times.

If the command set is a high level command set, the above described readprocess, would be implemented as a read special memory block command.The NDI device would need to be able know where to set its pointer toaccess the special memory block, set its pointer, know how big thespecial memory block is, and then send the special memory block. Thisprotocol offloads many of these tasks, such as keeping track of wherespecial memory information is stored, and how big the block sizes of thespecial memory information is, and where to store special memory data,from the NDI device. These tasks are performed by the bus controllerinstead by stringing low level instructions like set memory pointer andread and write memory together.

As discussed, the NDI device of the present invention operates inconjunction with a protocol that has a fixed, low-level, and lowoverhead instruction set that, in turn increases the actual data rate onthe network bus when used with smart sensors and actuator. Networktraffic for networking sensors and actuators is different from regularcomputer network traffic. Computer networks need to transfer large datafiles or messages from one computer to another. Consequently they havechecksums and block sizes associated with the messages to ensure robustand error free data transmission. These checksums and block sizes, orother overhead, associated with these computer network protocols is nota problem because the size of the overhead is small compared to thetotal message size. Network traffic for sensors and actuators isdifferent because in many cases, most of the messages on the network arevery small messages with only 16 bits of data. If a block size,checksum, or other unnecessary overhead is added to the small 16 bitdata message, the checksums, blocksize, and other overhead can containmore bits than the actual 16 bit data message. This effectively reducesthe bandwidth of the sensor and actuator network bus. The NDI devices ofthe present invention solve this problem by using a message protocolthat does not add any unnecessary overhead such as checksum and blocksize to short 16 bit messages. The only overhead added to these short 16bit messages is a sync pattern to indicate the start of a message, aflag bit, and a parity bit. The parity bit is used to check for errorsin the 16 bit message. The flag bit indicates if an error conditionexists in the sending NDI device or associated data channel.

The protocol of the present invention is typically transmitted in aManchester encoded format, but may also be implemented in a UniversalAsynchronous Receiver Transmitter (UART) format protocol, if needed, tocommunicate with other UART systems. For example, in one embodiment, theprotocol uses an RS-485 based, multi-drop, Manchester encoded protocolreferred to as Bi-Phase Sensor and System (BiSenSys). BiSenSys is an18-bit high speed, highly efficient protocol for use in connectingremote devices and subsystems together on a digital bus structure thatuses Manchester encoding. An example of another protocol that usesManchester coding is MIL-STD-1553. Specifically, each bit of the data isdetectable by one detectable transition, (i.e., “0” is defined as low tohigh and “1” is defined as high to low). Further, each message consistsof a sync pattern, a message body, and a parity flag. The BiSenSystransmission protocol can be operated in synchronous or asynchronousmode and the can be implemented to operate at any data rate from 1 Hz-10MHz in the synchronous mode or at 1.25, 2.5, 5.0, and 10.0 megabits persecond in asynchronous mode. Additionally, the protocol of the presentinvention may be implemented in a UART based protocol. This protocol isdesigned to operate at a 1.0 megabit per second data rate and uses a9-bit message format and non-return-to-zero bit coding.

There are at least three types of data frames transmitted across thenetwork bus, with the data frames differing between the BiSenSysprotocol and the UART protocol. There are 3 types of BiSenSys dataframes. The first type is a command frame. A command frame consists of acommand sync pattern followed by 10 Manchester encoded address bits,followed by 7 Manchester encoded command op-code bits, and 1 Manchesterencoded parity bit. The command sync consists of the one and a half busbit periods high and one and a half bit periods low state on the bus.

The second type of frame is an argument frame. An argument frame beginswith a data sync pattern which is followed by 16 Manchester encodedargument bits, one Manchester encoded flag bit, and finally oneManchester encoded parity bit. The data sync pattern consists of the oneand a half bit periods low followed by one and a half bit periods high.The last type of BiSenSys frame is the data frame. Data frames beginwith the data sync pattern, which is followed by 16 bits of Manchesterencoded data, one Manchester encoded flat bit, and one Manchesterencoded parity bit. The only difference between an argument frame and adata frame is that argument frames are transmitted by the bus controllerdata frames are transmitted by network devices. Arguments are onlytransmitted by the bus controller following certain commands. Thecommands that require an argument to follow them are defined in theRHAMIS/BiSenSys protocol. If the bus clock is used in the BiSenSyssynchronous mode, it is transmitted in quadrature to the Manchesterencoded bit stream.

In the case of the UART protocol, the message format contains 3 or more11-bit frames. Each message has three required frames per message withtwo additional optional frames per message depending on the commandissued. The first bit in every frame is a start bit (set to 0), and thefinal bit of all frames is a stop bit (set to 1). The first frame in amessage is an address frame for the UART protocol. It is in the form of:a start bit, an 8-bit address field, an address bit set to 1, and a stopbit. The second frame in a UART message is a command frame. A commandframe consists of a start bit, a 7 bit command field, an unused bit, theaddress bit set to 0, and the stop bit. If argument frames belong in theUART message, they follow the command frame. They consist of a start bitfollowed by 8 argument bits, an address bit set to 0, and the stop bit.The last frame of a UART message is a checksum frame. It consists of astart bit, 8 bit checksum, which is the modulo 2 sum of the address,command, and data bits with no carry, an address bit set to 0, and astop bit.

In addition to providing a protocol having a low-level instruction setthat operates in either synchronous or asynchronous mode and differenttransmission protocols, the present invention also provides a method forassigning unique addresses to each data channel. As illustrated in FIG.1, in a typical networked system 30, there will be numerous datachannels connected to a plurality of different NDI devices, all of whichuse a common network bus for communication with the bus controller.Further, each of the network devices may have several data channels orseveral tasks that can be commanded by the NDI device. The protocol ofthe present invention provides three types of addresses for each datachannel of a network device. Specifically, each data channel on eachnetwork device can be assigned an individual logical address, a globaladdress, and if configured, a group mask.

The logical address is an address recognized by a single data channel ona network device or a single controllable task with a network device. Aglobal address, on the other hand, is recognized by all of the datachannels of all of all of the network devices, while a group address isrecognized by a subset of all of the data channels of all of the networkdevices. Data channels are not assigned group addresses. They areassigned group masks. Each bit in the group mask corresponds to a groupaddress. In this way a single 16-bit mask can be used to assign a datachannel to 16 groups. For example if the 1^(st) and 3^(rd) bit of thegroup mask are set to 1, the data channel recognizes itself as belongingto groups 1 and 3. It will respond to command messages having a groupaddress of either 1 or 3. These three different addresses are importantas they allow the controller to either communicate with an individualdata channel of one network device or a group of data channels, eitherin the same network device or in several network devices, or with all ofthe data channels of all network devices. Each of these addresses isdescribed in detail below.

The determination of the logical and group addresses may be by anyselected method. A preferred method is described in U.S. ProvisionalPatent Application No. 60/254,137 entitled: NETWORK CONTROLLER FORDIGITALLY CONTROLLING REMOTE DEVICE VIA A COMMON BUS and filed on Dec.8, 2000. This method uses the Universal Unique Identifier (UUID)associated with each network device. The UUID code is an 80-bit codethat is unique to every network device and is based on the location anddate the device was manufactured.

With reference to FIG. 3A, the UUID for network device of the presentinvention are typically stored in the NDI device's memory device 66.During the determination of the logical and group addresses, thecontroller sends various commands to the NDI devices of the presentinvention commanding them to access their respective memory device,analyze the individual bits of the UUID and either respond or remainsilent based on whether certain bits are 1 or 0. This allows the buscontroller to discover the UUID of every network device, one networkdevice at a time. Immediately after finding the UUID of a networkdevice, the bus controller will assign logical addresses and group masksto every data channel on that network device.

FIG. 8 is a flow chart of the steps taken by a network device using anNDI device, under control of the bus controller, to uniquely identifyitself to the bus controller. To begin a Device Inventory session NDIdevices are enabled using the Device Inventory Enable command. This putsthe NDI in the Device Inventory mode. (See step 700). If address “0”(the reserved global address for all devices) is specified in theaddress field, every network device on the bus will put itself into theDevice Inventory mode. If a currently assigned logical address isspecified in the address field, that network device will put itself intothe Device Inventory mode. If a currently assigned group address isspecified in the address field, all network devices belonging to thatgroup will put themselves into the Device Inventory mode.

Various function codes in the Device Inventory command are used duringthe UUID word search. The Device Inventory command with the New UUIDWord Search function code sets all Device Inventory session enableddevices into the UUID Word Search mode. (See step 705). Network deviceson the bus will not compete in a UUID Word Search unless they are in theUUID Word Search mode. Immediately after being commanded into the WordSearch Mode, the NDI device automatically proceeds by loading the leastsignificant bit of the UUID into a first register and a “1” into asecond register. (See step 710). When NDI devices are in the UUID WordSearch Mode they will respond to the two UUID Bit Competition functioncodes.

The Master Controller will issue the Device Inventory command with theUUID Bit Competition, No Dropout function code. All NDI devices willmake a decision based on this command. (See step 720). The NDI devicewill proceed to step 730 and make a decision bases on its bit inregister 1. If this bit is a “1,” (see step 730), the network devicewill remain quiet. If this bit is a “0,” the network device willtransmit a UUID pulse. (See step 740). The network device will then movethe evaluated bit (either a “1” or a “0”) into bit register 2, accessits next UUID bit and load it into bit register 1. (See step 760).

The Master Controller will listen for UUID pulses transmitted on thebus. When the Master Controller hears a UUID pulse it knows at least 1network device has a “0” for its current UUID bit. If the MasterController hears at least one UUID pulse, the next command it will issueis the Device Inventory command with the UUID Bit Competition, 1'sDropout function code. The NDI device will have to interpret the commandand make a decision. (See step 720). When a network device hears thiscommand and code, it will look at its UUID bit in register 2. (See step780). If this bit is a “1”, the network device will exit the currentUUID Bit Competition mode and quit competing in the UUID Word Search. Ifthe bit in register 2 is a “0”, the network device will look at the bitin register 1. (See step 730). If it is a “0”, the network device willtransmit a UUID pulse. (See step 740). If this bit is a “1”, the networkdevice will remain quiet. The network device will then move the bit inregister 1 into bit register 2, access its next UUID bit and load itinto bit register 1. (See step 780).

If the Master Controller does not hear any UUID pulse on the bus, theMaster Controller will know that all network devices still in UUID WordSearch mode have a “1” in bit register 2. In response to this, the nextcommand the Master Controller will issue is the Device Inventory commandwith the UUID Bit Competition, No Dropout function code. When a networkdevice receives this command it will remain in the competition withoutregard to what is in its registers. In response to the command alldevices in the competition will look at bit register 1. (See step 730).If it is a “0”, the network device will transmit a UUID pulse. (See step740). If it is a “1”, the network device will remain quiet. The networkdevice will move the bit in register 1 into bit register 2, access itsnext UUID bit and load it into bit register 1. (See step 760).

The UUID Bit Competition described in this section is repeated for all80 UUID bits. The Master Controller will have to issue a combined totalof 81 UUID Bit Competition function codes. (See step 750). The MasterController must issue the 81'st UUID Bit Competition function code sothat the last network devices on the bus can resolve who had the winninglast bit.

After the Device Inventory command with the UUID Bit Competitionfunction codes has been issued for a combined total of 81 times therewill be only one network device left in UUID Word Search mode. Thisnetwork device is the winner. (See step 770). This network device hasnow been uniquely identified to the bus controller and will respond withthe contents of a special memory location. (See step 780). The high byteof the special memory location will hold the protocol revision number,and the low byte will be the number of data channels on the networkdevice. The winning network device and the bus controller will know thenetwork device has won by winning all 81-bit competitions.

When the winning device has received the 81^(st) UUID bit competitionfunction code, the device will respond with a Bi-Phase compliant datafield containing the protocol version number and the number of channelsthe device has stored in its memory. (See step 780). The bus controllermay use this information to determine logical address channel assignmentin the winning device. The winning network device will unprotect itslogical address and group mask memory locations. (See step 790). The buscontroller will assign logical addresses and group masks immediatelyfollowing. (See step 800). If the data channel includes a plurality ofthe channels, the Master Controller will assign logical addresses andgroup masks to each channel. (See step 810). After the logical addressesand group masks have been assigned, the network device will exit thedevice inventory mode. The bus controller will repeat the UUID wordsearches until all network devices have been discovered, and a logicaladdress and group mask assigned to every channel. The bus controllerknows it has discovered all devices when the UUID if discovers in thebus is all 1's. No network device will ever have a UUID of all 1's.

As described above, each channel for each network device is providedwith a logical address that uniquely identifies the data channel.Further, there are group addresses that address a number of datachannels, and a global address that addresses all channels of allnetwork devices. The global address is used for the exchange of globaldata and commands. The group address is an address that is recognized bymultiple data channels of the network devices. Group addresses cause oneor more data channels to respond to the same command at the same time.It is possible to have only one data channel assigned to a groupaddress. Associated with the group address is a group mask stored in theaddress decoder 100. The group mask is a 16-bit word, where each bit setto 1 represents the groups that the data channel belongs.

As an example, in one embodiment, the global address is assigned0000hex. In this embodiment, if the address 0000hex is transmitted, allof the NDI devices will follow the command. This is typically used forresetting the system or testing the system. Further, in one embodiment,the group addresses are selected in the range of 0001hex to 000fhex. Inthis embodiment, when an address in this range is received by a NDIdevice, it will compare the group address with the group mask stored inthe address decoder register 100. If the bit in the group maskcorresponding to the group address is set, the NDI device data channelof the present invention will interpret and follow the commandassociated with the group address. For example, if the group mask storedin the device inventory register is 100000001100b in, the NDI devicebelongs to group addresses 000fhex, 0003hex, and 0002hex.

The group address scheme is designed to permit the user to set up timedeterministic triggers for groups of sensors or actuators at varioussample rates. Table 1 illustrates a group of sensors having differentsample rates and their group assignments, and Table 2 the sequence forpolling the devices. As can be seen from these tables, the data channelscan be grouped together such that they may be triggered simultaneouslybut at different sample rates.

TABLE 1 Logical Sample Rate Address Device (Samples/sec) Group Address16 Temperature 1 125 1 17 Pressure 1 250 1, 2 18 Strain 1 500 1, 2, 3 19Strain 2 500 1, 2, 3 20 Strain 3 500 1, 2, 3 21 Strain 4 500 1, 2, 3 22Accelerometer 1 1000 1, 2, 3, 4 23 Accelerometer 2 1000 1, 2, 3, 4 24Accelerometer 3 1000 1, 2, 3, 4 25 Accelerometer 4 1000 1, 2, 3, 4

TABLE 2 Command Execution Time Action 0 Issue Trigger Command to Address1 Poll Addresses 16 through 25 1 msec Issue Trigger Command to Address 4Poll Addresses 22 through 25 1 msec Issue Trigger Command to Address 3Poll Addresses 18 through 25 1 msec Issue Trigger Command to Address 4Poll Addresses 22 through 25 1 msec Issue Trigger Command to Address 2Poll Addresses 17 through 25 1 msec Issue Trigger Command to Address 4Poll Addresses 22 through 25 1 msec Issue Trigger Command to Address 3Poll Addresses 18 through 25 1 msec Issue Trigger Command to Address 4Poll Addresses 22 through 25 1 msec Restart Sequence

With regard to the group addresses, if the controller sends out a groupaddress, the address decoder 100 and a command decoder 102 of thepresent invention will decode the address portion of the command andwill compare the group address to group mask stored in itself. If thegroup mask indicates that the network device is subject to the groupaddress, the proper data channel will perform the command associatedwith the group address on the network device.

Described above, the addressing methods used with the protocol allowsthe controller to send commands and data to either one or several of thenetwork devices, with the different forms of data transmitted dependingon whether BiSenSys or UART is used. Provided below are the commandstypically used to communicate across the network bus. As statedpreviously, the protocol of the present invention is designed tomaximize efficiency so that the commands and response messages can varyin length depending on the data quantity required to execute anycommand. In order to accomplish this, the protocol of the presentinvention provides three levels of utility. These commands are listed inTable 3.

TABLE 3 Command (hex) Command Description Service Commands 00 No Op 01Built in Test 02 Reset 03 Read Status Register 04 Device InventoryEnable 05 Device Inventory 06 Control Pass 07 Wake 08 Sleep 09E-Calibration 0A Z-Calibration 0B Synchronize 0C Baud Select 0D-0FReserved Data Commands 20 Trigger 21 Trigger and Read 22 Read In-DataRegister Word 23 Read In-Data Stack Word 24 Read In-Data Stack Block 25Query In-Data/Out-Data Stack Depth 26 Write Out-Data Stack Word 27 WriteOut-Data Stack Word/Acquire to In-Data Register 28 Write Out-Data StackBlock 29-2F Reserved Memory Commands 30 Set Memory Pointer 31 ReadMemory Word with Current Pointer 32 Read Memory Block with CurrentPointer 33 Write Memory Word with Current Pointer 34 Write Memory Blockwith Current Pointer 35 Read Memory Word with Passed Pointer 36 ReadMemory Block with Passed Pointer 37 Write Memory Word with PassedPointer 38 Write Memory Block with Passed Pointer 39-7F Reserved

One level of commands is the service commands. Service commands areintended for network housekeeping, network device interface status,power control, calibration, and bus master arbitration. These commandsare briefly described below. For example, the No Op command instructsthe NDI device of the present invention to take no action. The No Opcommand is typically used in initialization of operation or by themaster or network controller, (see FIG. 1), to maintain bus control.

The Built-In-Test (BIT), E-Calibration, and Z-Calibration commands areused to perform self-test on the NDI devices connected to the networkbus. For example, the BIT command commands the NDI device to perform acheck of internal circuitry. The E-Calibration command forces anexcitation calibration, where the input from a sensor network device isreplaced with a reference voltage, and the NDI device takes a reading todetermine the calibration of the NDI device at the reference voltage.Similarly, the Z-Calibration command initiates a zero calibrationmeasurement, where the input for a sensor data channel is shorted. TheNDI device takes a reading to determine the offset of the data channel.

The protocol also includes two types of reset commands, namely Reset andSynchronize. The Reset command initializes all the network deviceinterfaces of the present invention that are connected to the networkbus to a power-up state. This Reset command is typically used by thecontroller to reset the bus and network devices when necessary andregain control of the network bus.

The Synchronize command is an important command for establishing andmaintaining synchronization between several NDI devices. Specifically,as discussed previously, some A/D and D/A converters require acontinuous clock signal that is different from the synchronous clocksignal provided by the controller. This clock signal is provided by adivider that divides down either the synchronous bus clock signal or theclock signal from a local oscillator. This divided clock signal is usedby the converter to convert data. Although the divider provides theproper clock frequency needed by the converter, the presence of thesedifferent dividers on the different NDI devices can cause the converteron one NDI device to not be synchronized with a converter on another NDIdevice. Specifically, all of the converters may be operating at the samefrequency, but the dividers may be out of phase.

In light of this, the Synchronize command synchronizes the divided clocksignal among a plurality of NDI devices. Specifically, with reference toFIG. 9, when the divider is using the synchronous clock signal and theSynchronize command is issued, the NDI device will control its clockdivider to reset and restart producing the clock signal. All of the NDIdevices will do the same reset and restart of their clock dividers atthe same time according to the group or global address used in thesynchronize command.

FIGS. 11 a, 11 b, and 11 c illustrate alternative embodiments of how theNDI device of the present invention can be attached to and controldifferent data channels. Some data channels will only need the convertsignal from the NDI device to acquire data with precise timing as inFIG. 11A. Some data channels will need only the synchronized dividedclock and possibly the synchronize signal to acquire data with precisetiming in FIG. 11B. Some data channels, such as in FIG. 11C may requireboth the convert and divided clock signals to acquire data with precisetiming.

With reference to FIGS. 11A-11C, the use of the Synchronize command isillustrated with respect to causing switched capacitor filters 126,sigma/delta A/D converters 120, or digital filters 118, etc. in the datachannels among different network devices to all operate synchronously.If the clock divider is dividing the local oscillator to produce theclock signal, the divider will reset and restart at the center edge ofthe parity bit of the synchronize command. This will cause the clockdividers among a plurality of NDI devices to synchronize together. It isrealized that the clocks will drift out of phase over time howeverbecause of variations in the frequencies of the local oscillators. Ifthe source for the clock divider is the bus clock, the clock dividerswill synchronize according to the timing in FIG. 9, and the dividedclocks will continue to run synchronously after that. The currentembodiment of the NDI device provides the synchronize signal, 116, 124,and 128, to the data channels attached to it to reset or synchronizesigma/delta A/D converters 120, digital filters 118, or other devices.

With reference to Table 3, the protocol also includes Wake and Sleepcommands. The Sleep command powers down certain portions of the networkdevices and the Wake command powers them up. Further, the protocolincludes the Read Status Register command. This command provokes a readof the status register of the NDI device and provides information, suchas whether the network device is busy, whether it supports certaincommands, whether the controller requested to much or too little datafrom the data stack, whether message transmission errors have occurred,whether the memory is unprotected, etc.

The Control Pass command is used by the master and network controllersto establish which bus controller is in control of the bus, if there ismore than one bus controller on the network bus. Further, the BaudSelect command can be used by the controller to change the baud rate onthe network bus when operating in the asynchronous mode.

The Device Inventory Enable command and the Device Inventory commandwere previously discussed in relation to the unique identification ofevery network device and the assignment of logical addresses and groupmasks to the data channels. The Device Inventory Enable command selectsgroups of network devices to be inventoried. The Device Inventorycommand is used to control most actions associated with identifyingnetwork devices and assigning logical addresses and group masks. Thecommand is different in that the address field of the command is used todirect various device inventory functions within a device. For example,these functions include entering into a new Word Search competition andthe actions associated with No Dropout and I's Dropout. Further, thecommands include reading from the memory of the device that won the WordSearch and writing the logical addresses and group masks.

A second type of commands is data type commands. These commands aretailored for time-deterministic data acquisition and control. Networkefficiency is maximized by permitting NDI devices to move one data pointdirectly or more than one data point as defined-length block transfers.For example, the Trigger command is used by the controller to initiatean incoming data measurement in a sensor data channel or cause a dataconversion to a physical quantity in an actuator data channel. Withreference to FIG. 3B, each of the channels of the network deviceinterface of the present invention includes an In-Data Register 89 andan In-Data Stack 88. When the Trigger command is received by the NDIdevice, the contents of the In-Data register are pushed to the top ofits In-Data stack. It will then take a new reading from the datachannel. When finished reading, the new reading will be in the In-Dataregister. The bus controller will normally read data from the in-datastack.

While acquiring data from the In-Data stack causes a latency of one ormore sample in the sensor reading sent to the bus controller, thisarrangement allows Read-in-data-stack commands to be issued to a sensordata channel immediately after a Trigger command. Read in-data stackcommands read data from the in data stack. This, in turn, allows maximumuse of the network bus bandwidth, which is important where sensor datachannels have long conversion times. This also simplifies the Triggerand Read command set that the user must write because pauses do not needto be included before reading from the in-data stack.

The Read In-Data Register Word command permits reading data from theIn-Data register immediately after it becomes available from the datachannel. The bus controller must not try to read from this registerbefore the data becomes valid. In the case where the network device isan actuator, the NDI device will command a data conversion on the valueat the top of the Out Data Stack and then pop the Out Data stack. In thecurrently implemented embodiment of the NDI device, not shown here,there is not out-data stack in the NDI device. The data is sent from thebus controller to the NDI device and straight to the D/A converter ordata channel without passing through a data stack. However the D/A ordata channel connected to the NDI device has a register to hold the datawhich serves as an out-data stack with a size of one stack word.

As discussed, the Trigger and Read command is used to initiate ameasurement cycle of a data channel and immediately transmit the resultsof the previous measurement on the network bus. In response to thiscommand, the NDI device of the present invention simultaneously pushesthe contents of the In-Data register onto the In-Data stack, begins anew measurement cycle, and begins transmitting the contents of the topof the In-Data stack. The push to the In-Data stack will occur beforeand during the transmission of the data sync pattern of the command. Inthis way, the result of the previous measurement will be valid and inthe data stack when the transmitter section of the NDI device accessesit for transmission. The data sample is then transmitted across thenetwork bus while a new measurement is taken.

With regard to the read commands, the Read In-Data Register Word commandinitiates a read directly from the In-Data register. The NDI deviceplaces the contents of the In-Data register on the network bus. The ReadIn-Data Stack Word command is used to read a data word from the top ofthe In-Data stack. In this instance, the NDI device of the presentinvention responds by outputting the newest data word from the datastack onto the network bus and older data is shifted to the top of thestack.

As illustrated in FIG. 3B, the data stack associated with each channelof the NDI device of the present invention includes several registers.The Query In-Data/Out-Data Stack Depth command is used to determine howmany valid data words are on the In-Data or Out-Data stack. In thisinstance, the NDI device of the present invention keeps track of thenumber of valid data words in its stack depth register. The value ofthis register is transmitted to the bus controller by the NDI devicewhen commanded by the bus controller.

The Write Out-Data Stack Word command directs the NDI device of thepresent invention to write a data word to the top of the Out-Data stack.Further, the Write Out-Data Stack Word/Acquire To In-Data Registercommand further directs the NDI device to simultaneously acquire datafrom the data channel and put it into the In-Data register. If theoutput signal to the data channel is connected to input to the NDI fromthe data channel, this command can be used to echo data sent to theactuator back to the bus controller. Similar to the Write Out-Data StackWord, the Write Out-Data Stack Block command directs the NDI device towrite multiple data words to the Out-Data stack.

In addition to the service and data type commands, the protocol of thepresent invention also includes memory commands. These commands permitaccess to specific defined memory locations or functions to which datacan be written or read. This permits random access data blocks to beefficiently transferred between one system and another with littleoverhead. It also permits direct memory access and/or one or more databuffers blocks to be moved.

For example, the command Set Memory Pointer sets the memory addresspointer within the NDI device. The Read Memory Word With Current Pointercommand is used to read a single word from memory pointed at by thememory address pointer. The Read Memory Block With Current Pointer isused to read a block of data words from memory starting at the memoryword pointed to by the current value of memory address pointer. Anargument passed with the command to the NDI device instructs the NDIdevice as to how many data words are to be read. After each memory wordis sent to the bus controller by the NDI device, the memory pointer isautomatically incremented by one. Then the next memory word istransmitted. This process is repeated until the number of memory wordsrequested by the bus controller has been transmitted.

The protocol of the present invention also includes write memorycommands. Specifically, the Write Memory Word With Current Pointercommand writes a single word into memory. The NDI device will write theargument accompanying the command into memory at the location currentlypointed to by the memory address pointer. The Write Memory Block WithCurrent Pointer command, on the other hand, writes a block of data wordsinto memory. The NDI device of the present invention will write thearguments accompanying the command into memory beginning at the locationcurrently pointed to by the memory address pointer. After each word iswritten, the memory address pointer is incremented by one. This processis repeated until all of the words have been written into the memory.

Similar to the commands just described, the protocol of the presentinvention includes commands for reading and writing words and blocks ofdata from and into memory using a pointer sent by the controller alongwith the command. These commands operate similar to those above, exceptthe pointer is provided as an argument following the command. Thesecommands are: Read Memory Word With Passed Pointer, Read Memory BlockWith Passed Pointer, Write Memory Word With Passed Pointer, and WriteMemory Block With Passed Pointer.

As stated previously, the NDI device of the present invention providesfor digital communication of commands and data between a controller andvarious network devices across a network bus. With regard to FIG. 10, anetworked system implementing the NDI device of the present invention isillustrated in an aircraft 10. In this embodiment, a network is used tomonitor various critical structural locations. Located on the aircraftare network devices to measure strains 12, such as wing root, wingsurface, tail root, tail cord and landing gear strains, andaccelerations 14, such as wing tip and tail tip accelerations. Further,the network includes sensors 16 to monitor the pressure at variouscritical structural locations, such as critical belly pressures forsonic fatigue, as well as key corrosion locations 18 for radar, landinggear and leading edges, and engine casing temperatures 20. In thisembodiment, all of the network devices are connected to a common bus,thereby eliminating excess wiring. Further, data and commands aretransmitted digitally to reduce susceptibility to noise.

Additionally, the preferred protocol for the NDI devices uses Manchesterencoding of network data bits to help allow miniaturization of the NDIdevices. It must be understood that for any device to receiveasynchronous serial data, it must be able to acquire the timing of thedata sequence from the serial data stream. Normally, the receiver of theserial asynchronous data must have a local oscillator to cause itsreceiver to operate, and recover the timing information from the serialdata. Once the timing information has been extracted, the asynchronousreceiver is able to receive serial data at certain rates, plus or minusa certain deviation from these rates, given this local oscillatorfrequency. Manchester encoding of serial data causes a transition fromhigh to low or low to high in the center of every bit. This makes iteasy to extract the necessary timing information from the serial datastream. Because it is so easy to extract the timing information from theManchester encoded serial data stream, a relatively large deviation fromthe expected data rate, based on the local oscillator can be tolerated.This tolerance to relatively large deviations from the expected datarates allows each NDI receiver to use a low accuracy local oscillator toreceive the Manchester encoded data. Low accuracy local oscillators canbe made extremely small. Current embodiments of adequate localoscillators are only about 1×1.5 millimeters. This aids in makingminiature NDI devises.

Many modifications and other embodiments of the invention will come tomind to one skilled in the art to which this invention pertains havingthe benefit of the teachings presented in the foregoing descriptions andthe associated drawings. Therefore, it is to be understood that theinvention is not to be limited to the specific embodiments disclosed andthat modifications and other embodiments are intended to be includedwithin the scope of the appended claims. Although specific terms areemployed herein, they are used in a generic and descriptive sense onlyand not for purposes of limitation.

1. A protocol stored on a computer-readable medium for transmittingcommands and data between a bus controller and a network deviceinterface across a common digital network, wherein said protocolcomprises a set of low level instructions for sending respectivecommands and data such that it is possible to implement at least one ofthe bus controller and the network device interface as a state machine,wherein said protocol uses messages having bit lengths that vary basedon at least one of the command and data being transmitted in themessage.
 2. A protocol according to claim 1, wherein said protocolcomprises a set of low level instructions such that one of theinstructions cause at least one of the bus controller and network deviceinterface to perform a single operation only.
 3. A protocol according toclaim 1, wherein said protocol uses low level instructions requiringless processing such that at least one of the NDI device and the buscontroller is a state machine implemented as either an ApplicationSpecific Integrated Circuit (ASIC) or a field programmable gate array(FPGA).
 4. A protocol according to claim 1, wherein said protocolincludes at least one of a command and a data structure for sendingrespective commands and arguments to the network device.
 5. A protocolaccording to claim 1, wherein said protocol uses messages that areindependent of an information representing a block size for the messageor a checksum for the message.
 6. A protocol according to claim 1,wherein said protocol uses messages that contain data representing async pattern that is used to synchronize with the message.
 7. A protocolaccording to claim 1, wherein said protocol uses messages that containdata representing a flag bit that indicates if an error condition existsin the network device interface.
 8. A protocol according to claim 1,wherein said protocol uses messages that contain data representing atleast one parity bit that is used to check for errors in the message. 9.A protocol according to claim 1, wherein if a command includes more thanone instruction, said protocol separates the command into each separateinstruction and sends each instruction one at a time.
 10. A protocolaccording to claim 1, wherein said protocol is transmitted in one of aManchester encoded format and a Universal Asynchronous ReceiverTransmitter (UART) format protocol.
 11. A protocol according to claim 1,wherein said protocol sends commands in the form of a command framecomprising: bits representing a command sync pattern; bits representingan encoded address; bits representing an encoded command; and an encodedparity bit.
 12. A protocol according to claim 1, wherein said protocolsends argument information in an argument frame comprising: bitsrepresenting a data sync pattern; bits representing an encoded argument;an encoded flag bit; and an encoded parity bit.
 13. A protocol accordingto claim 1, wherein said protocol sends data information in a data framecomprising: bits representing a data sync pattern; bits representingencoded data; an encoded flag bit; and an encoded parity bit.
 14. Amethod for transmitting commands and data between a bus controller and anetwork device interface across a common digital network comprising thestep of transmitting commands and data using a set of low levelinstructions such that it is possible to implement at least one of thebus controller and the network device interface as a state machine,wherein said transmitting step uses protocol having messages with bitlengths that vary based on at least one of the command and data beingtransmitted in the message.
 15. A method according to claim 14, whereinsaid transmitting step comprises transmitting commands and data using aset of low level instructions such that one instruction causes at leastone of the bus controller and network device interface to perform asingle operation only.
 16. A method according to claim 14, wherein saidtransmitting step uses protocol that includes at least one of a commandand a data structure for sending respective commands and arguments tothe network device.
 17. A method according to claim 14, wherein saidtransmitting step uses protocol that contains messages that areindependent of an information representing a block size for the messageor a checksum for the message.
 18. A method according to claim 14,wherein said transmitting step uses protocol containing messages thatcontain data representing a sync pattern that is used to synchronizewith the message.
 19. A method according to claim 14, wherein saidtransmitting step uses protocol containing messages that contain datarepresenting a flag bit that indicates if an error condition exists inthe network device interface.
 20. A method according to claim 14,wherein said transmitting step uses protocol containing messages thatcontain data representing at least one parity bit that is used to checkfor errors in the message.
 21. A method according to claim 14, whereinin said transmitting step if a command includes more than oneinstruction, said transmitting step separates the command into eachseparate instruction and sends each instruction one at a time.
 22. Amethod according to claim 14, wherein said transmitting step transmitscommands and data in one of a Manchester encoded format and a UniversalAsynchronous Receiver Transmitter (UART) format protocol.
 23. A methodaccording to claim 14, wherein said transmitting step sends commands inthe form of a command frame comprising: bits representing a command syncpattern; bits representing an encoded address; bits representing anencoded command; and an encoded parity bit.
 24. A method according toclaim 14, wherein said transmitting step sends argument information inan argument frame comprising: bits representing a data sync pattern;bits representing an encoded argument; an encoded flag bit; and anencoded parity bit.
 25. A method according to claim 14, wherein saidtransmitting step sends data information in a data frame comprising:bits representing a data sync pattern; bits representing encoded data;an encoded flag bit; and an encoded parity bit.